Preparation of uranium-niobium alloys by co-reduction



of the metal and the slag produced by the reaction.

United States Patent l 3,301,667 PREPARATION OF URANIUM-NIOBIUM ALLOYS BY (IO-REDUCTION Waldo R. Golliher and Robert A. Johnston, both of Paducah, Ky., assignors to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Filed Apr. 27, 1966, Ser. No. 546,479 3 Claims. (Cl. 75-122.7)

The invention described herein was made in the course of, or under, a contract with the U.S. Atomic Energy Commission. The present invention relates to and has for its principal object the preparation of uranium-niobium alloys by bomb reduction in an essentially adiabatic process. I

' In order to produce an alloy of uranium by bomb reduction methods, a mixture ofuranium tetrafluoride, a reducible salt or oxide of the alloying metal, and a coreductant such as magnesium must be uniformly blended, packed into a refractory-lined container, and heated by external means until the reaction occurs. The resultant mass of metal that collects at the bottom of the lined cavity as one piece is known as a derby. The refractory lining and bomb container must meet several specifications to ensure good quality and yield of the alloy metal. These requirements are well-known to those skilled in the art. Briefly, it is that the refractory liner is primarily used to contain the alloy formed by the reaction and to protect the .alloy from contamination by the bomb shell material. Since it comes in contact with the alloy formed, it must be relatively free of impurities that would unite with the alloy to impair its quality. After the liner is formed inside the bomb it must have suflicient green strength to have a charge packed into the resultant cavity without mixing with the charge. It must also have suflicient fired strength at the time of reaction to resist mixing with the reaction mass and thereby cause an inefficient separation One material that adequately meets this requirement is magnesium fluoride slag produced by the reaction as a byproduct of UF by magnesium. An even more useful liner material is magnesia, MgO, because of its higher temperature stability and chemical inertness.

The initial source material for the metals of the alloys to be formed which can be used are limited to those which are reducible by a common reducing agent such as magnesium or mixture of calcium with iodine to effect total reduction of the respective source materials in a controllable and essentially adiabatic chemical reaction. The use of uranium tetrafiu-oride for chemical co-reductions of this 1 type is well known and does not form a part of this invention per se. The essential and controlling choice is the niobium source material used in the c-o-reduction.

The salt of the metal chosen for the co-reduction with UF, must be anhydrous, have a low vapor pressure at high temperatures near the reaction temperature with magnesium, and be avail-able in sufliciently high purity so as not to grossly contaminate the resultant alloy with undesirable elements. Furthermore, it should be reducible in a reaction with magnesium or calcium thatis not so highly reactive as to be dangerous. A still further requirement is that the alloy salt must be sufliciently stable up to a point of reaction so that it does not either inhibit the reaction or decompose prior to the desired reaction.

Moreover, the fluoride reaction products of such a salt It is the object of this invention to supply the foregoing 3,301,667 Patented Jan. 31, 1967 requirements by effecting an essentially adiabatic bomb co-reduction of a mixture of '(1) uranium tetrafluoride and. (2) a composition selected from either (a) a mixture of potassium fluoniobate and from 050%, by weight, based on the niobium of niobium pentoxide, Nb O or (b) the reaction product resulting from a reaction between niobium pent-afluoride and a fluoride salt selected from cesium fluoride, lithium fluoride, barium fluoride, calcium fluoride, uranyl fluoride, potassium fluoride, and magnesium fluoride.

The generic concept of this invention lies in the discovery that a particular class of selected niobium fluoride salt composition-can be used in an essentially adiabatic co-reduction processpf forming uranium-niobium alloys at a temperature much lower than is required for directly melting the respective elements of a desired alloy. What this invention provides is a reducible niobium salt as the initial niobium source which generates a heat of reaction with magnesium at least as great as that eflected by the reduction of UF and magnesium to produce a low melting magnesium fluoride slag. This allows as much of a clean-cut slag-derby separation as is possible for such co-reductions while obtaining an alloy of desired composition. An ancillary concept of this development relates to the discovery that niobium pentafluoride, by itself a hygroscopic low melting compound, can be upgraded to a non-hygroscopic, high melting fluoride salt complex composition by reaction with the selected metal fluorides previously mentioned.

The selection of the proper niobium source material and success of the process lies in the recognition that the selected fluoride salts are stable and non-hygroscopic, as well as reducible under the same conditions required to reduce uranium tetrafluoride. Moreover, the secondary reaction product is, for the most part, magnesium fluoride which does not interfer with, or introduce any extraneous by products which would tend to increase the melting point of the slag, or prevent its separation from the derby after it is formed. I

Once the selected source materials are chosen to produce an alloy of desired composition, the efficiency of the co-reduction depends on the bomb firing conditions. With the reactants at room temperature, the heat of reaction is generally insufficient under adiabatic conditions to initiate and maintain the reduction products molten until an efliecient separation has been eflected between the mass of alloy derby and the resultant magnesium fluoride slag. Consequently, a resistance or induction-type furnace is used to initiate the reaction and to add the required heat to the" reaction products to bring about an eflicient sep- As a result, the firing schedule consists of preheating the mixture in the bomb at a low temperature such as 1300 F. for a period of time depending upon the quantityof heat required until the charge fires. In addition to the firing time, other variables that will influence the yield and quality of massive metal alloy derby from the reaction will include the reductant used, such as magnesium or calcium metal, or calcium mixed with a quantity of iodine; the melting point of the slag produced by the reaction and the'melting point of the alloy itself to produce a sound substantially pure uranium-niobium alloy derby by reduction of UF and a selected niobium fluoride salt with magnesium. The optimum conditions are 7 to 10 stoichiometric exces of magnesium, 01% of the uranium as UO F with a furnace control temperature set at from 1200 F. to 1300" F. In terms of producinga high quality derby alloy in which quality is determined by size, weight, and shape of the derby, amount of voids, amount of slag inclusions, and the degree to which the desired composition is realized, the preferred niobium salt is a mixture in which 50% of the niobium is obtained from Nb O and the remainder from KzNbFq.

4 contained numerous small voids and slight inclusions of incompletely separated slag. As the amount of K2NbF7 increased to 100% the derbies contained increasingly larger voids and slag inclusions. Nevertheless, the der- The following examples illustrate the rnethod of co-re- 5 bies were of excellent quality and could readily be conduction under essentially adiabatic conditions to produce verted to a highly purified alloy ingot by a simple and a quality alloy derby in accordance with the general destraightforward melting operation for a time sufiicient scription prevoiusly provided. to allow separation of slag inclusions and removal of voids.

A purified a-lloy casting is then obtained by bottom pour- Example I ing into a casting mold. As shown in the table, no derby was formed when all of the niobium in the charge was In this and the following examples the materials used present as NbzOE. were ingot magnesium supplied by the New England Lime Company, UF made by the reduction of UF with hy- E l H drogen, high purity 200 mesh niobium pentoxide, and xamp e 200 mesh potassium fiuoniobate, KgNbFq, obtained from Kawecki Chemical Company. The co-reductions As previously mentioned, an ancillary generic concept were made in steel bombs designed to produce a derby of this invention is concerned with the provision of a weight of about 4 kilograms. Magnesium fluoride liners unique class of stable complex niobium fluoride salts by were provided by jolting magnesium fluoride powder into reaction of the volatile, hygroscopic niobium pentafluoride, the shell with a pneumatic mechanism. A globar re- NbF with selected stabilizing metal fluoride salts to prosistance furnace Was used to heat the bomb. The reducduce a non-hygroscopic complex fluoride composition tion bomb was instrumented with external thermocouples which is far more stable than niobium fluoride, wherein which indicated the bomb shell temperature at the botits stability depends on the relative amounts of the statom, middle, and top. A thermocouple was inserted into bilizing metal fluoride additive. The several selected metthe charge to measure the temperature in the center of al fluorides are dried in fluorine and then mixed at varythe charge. UR; and other constituents of the bomb ing mole ratios with niobium pentafluoride in adryatmoscharge were thoroughly mixed in a V-type blender and phere. Each mixture was placed in a nickel reactor. charged into the magnesium fluoride lined shell. The The reactor was then evacuated to a partial vacuum of charge was compacted and a magnesium fluoride liner about 0.1 millimeter mercury and heated to 400 F. for was placed on top of it. A metal lid was then put in 4 hours to allow reaction to occur. After this, the reacplace and the bomb placed in a pre-heated furnace. The tion mixtures were cooled and the resulting compositions bomb temperatures were recorded and the time for the Were determined on the basis of weight change and chembomb to fire was noted. After the reaction was comical analyses. The thermal stability of each material was pleted, the bomb was cooled and the contents were redetermined by testing for weight changes using a thermoved, balance at temperatures ranging from 5001400 F. The

The following describes the subject process as used to resultant data obtained is summarized in Table II. produce a uranium-6 wt. percent niobium alloy derby.

4906 grams of UF 54 grams of UO F 393 grams of KzNbFq, and 172 grams of Nb O were thoroughly blended with i008 grams of Mg, and the blend was charged TABLE nrNbFyMETAL FLUO RIDE COMPLEXES into a MgF -lined steel reduction bomb sized to produce a 4kg. uranium-derby. After the powder charge had been compacted and then capped with a layer of MgF the bomb was closed with a steel lid and inserted in a resistance-heated furnace preheated to 1300 F. The bomb Condltlons pp Composition Time, Decomwas instrumented to record its shell temperature and the Hm position temperature at the center of the charge. The following p-f table summarizes this reduction run (indicated by an d As Pre are 0.770 F -NbF 300 asterisk) as well as several related runs. Stable g 500 F 1 24 Z Z Z 7 4 550 Stable at 800 1 74 CaFz-NbF5" 3. 0 900 Stable at 1,000 F 4.00 CaFz-NbR" 2. 0 1, 275 TABLE 1 Stable at i,400 8.03 Car -Note... 0. 5

A eTe t w Run Nb as h i r ing, a Pre-ignition Yield, LIP No. K NbF1% Time, Min. Percent 2 Conditions A Center Composition 'Iiii1e, D1223;- Hrs. positiop 0 3 1,100 39 4 Temp, F. 0 i 2Z 8 13 1 (4) 99 s 50 5 *50 1,210 1,225 03 99.8 gi fi g gggiga 75 1,125 1,210 80 100+ Stable at 0 R 153 sts its is 22-2 at F 100 950 1:140 73 Stable at 1,400 L1 100 900 1,160 69 99.9

BaFz 1 The remainder of the niobium was added as NbiO 2 Contains some entrapped slag. Furnace pro-heated to 1200 F. Conditions 4 Approx. 4N0 Derby. Composition Time, Decom- Hrs. position Temp.. F.

The best quality derbies were obtained from runs 3-6 P d 4B F Nbr in which the niobium was provided in theform of at least AS r 8'2 Z Z Z" 0'2 228 50%, by weight, KgNbFq with the remainder being nio- 124 BaFz-Nbgs 2.0 000 bium pentoxide These derbies had a density approach- Stable atmoos g g {9? ing the theoretical density of the alloy composition but TABLE II.Cntinue(1 for an adiabatic co-reduction with uranium tetrafluoride to produce a desired uranium-niobium alloy.

02 22 Example III Conditions 7 Approx. This example illustrates the applicability of a complex Commsmon fi i giggly double fluoride of niobium as prepared in Example II.

Temp.,F Two complex fluoride compositions synthesized according to the procedure of Example II were mixed with ap- As1 repared 0.44 UOzFz-NbF; 300 propirate amounts of uranium tetrafluoride and reduced 288, g" g g? 8g 83g in an adiabatic bomb reduction reaction as described in Stable at 1,000: if: 6 71 UoeFe-Nbre 0. 5 1,100 Example I. The results are tabulated in Table III below. Stable U02F1111Y For purposes of comparison, runs 5 and 6 were conducted with the preferred niobium source (5 0-5 0 mixture TABLE III Percent Niobium Added As Firing Derby Run No. Time Density (Min.) (g./cc.)

0. S7 BaFn-NbFz, 2. 11 CaFz-NbFs K2NbF7 Nbzoti F of Nb205+K2NbF7). The diflerences are reflected in the K derby density, a higher density indicating less porosity and/ or slag inclusion. All derbies contained the pre-cal- Composition Time, gggg fl' culated alloy composition and can be melt casted to pro- Hrs. positio n duce high purity alloy mgots.

Temp" Having thus described our invention, we claim:

P d 0 86 KF NW 150 1. A method for synthesizing a uranium-niobium alloy s' I Z: "5;;- 600 which comprises effecting an essentially adiabatic bomb Stable at800 g 1.14 lgg ggge- 6.3 950 co-reduction of a mixture of (1) uranium tetrafiuoride 22:21:22 no 51;; a.ae:NbF:;;;. 2;? .1119? end e e e e eeleetee free either e e ture of potassium fluomobate and from 0-50% by weight (based on the niobium of niobium pentoxide), Nb O MgFZ or (b) the reaction product resulting from a reaction be- A tween niobium pentafluoride and a fluoride salt selected Conditions pprox.

Composition Time, Dewy from cesium fluoride, lithium flu0r1de, bar1um fluoride, Hrs, posltugl 40 calcium fluoride, uranyl fluoride, potassium fluoride, and

Temp-r magnesium fluoride. I- W 2. The method according to claim 1 in which the source As Prepared 0.83NgFz-N 5 200 Stable at F" 0'86 MgFrNbFsu 0.7 600 of niobium is derived equally from potassium fiuomobate l '%tt i '2 1 $88 and Nbzofi Sta eat 1,000 5. l g r s 1. Stable at 1,40o 14.1MgF -NbF 0.7 T method 9 to l m} 1 Whlch 1% by Weight of the uranium in the initial mixture 1s m the form of UO F uranyl fluoride.

References Cited by the Examiner Nuclear Science Abstracts, vol. 14, No. 10, May 31, 1960, Abstract No. 9713, p. 1234.

Reactor Core Materials, vol. 1, N0. 2, May 1958, p. 4.

CARL D. QUARFORTH, Primary Examiner.

M. J. SCOLNICK, Assistant Examiner. 

1. A METHOD FOR SYNTHESIZING A URANIUM-NIOBIUM ALLOY WHICH COMPRISES EFFECTING AN ESSENTIALLY ADIABATIC BOMB CO-REDUCTION OF A MIXTURE OF (1) URANIUM TETRAFLUORIDE AND (2) A COMPOSITION SELECTED FROM EITHER (A) A MIXTURE OF POTASSIUM FLUONIOBATE AND FROM 0-50%, BY WEIGHT (BASED ON THE NIOBIUM OF NIOBIUM PENTOXIDE), NB2O5, OR (B) THE REACTION PRODUCT RESULTING FROM A REACTION BETWEEN NIOBIUM PENTAFLUORIDE AND A FLUORIDE SALT SELECTED FROM CESIUM FLUORIDE, LITHIUM FLUORIDE, BARIUM FLUORIDE, CALCIUM FLUORIDE, URANYL FLUORIDE, POTASSIUM FLUORIDE, AND MAGNESIUM FLUORIDE. 